This invention relates generally to controllers for controlling a number of electrical devices in response to control inputs received from a number of control input sources, and, more particularly, to such an electrical controller wherein electrical isolation is maintained between each of the control input sources.
The need to control a number of electrical devices in response to control inputs received from a number of sources, and, in particular, to control relatively few electrical devices in response to control inputs received from relatively many sources, can occur in a variety of control system installations. In automative gasoline and diesel-fuel filling stations, for example, several individual fuel hoses or dispensers are typically supplied with fuel provided from a single submersible pump fitted to a common underground storage tank. In larger filling stations, it is not uncommon for as many as eight underground storage tanks to supply fuel to as many as forty-eight hoses. Thus, several control input sources can exist for actuating the submersible pump of each storage tank.
To provide for the selective actuation of individual submersible pumps in response to control inputs received from a number of sources, various systems have been developed. In one such system, individual electrical switches, associated with each of the hoses or dispensers supplied from a common tank, are commonly connected to each other and to the coil of an electrical relay which controls the application of power to a submersible pump fitted to the tank. Although this system is effective in inexpensively implementing the desired control effect, it suffers the serious disadvantage of promoting undesirable "feedbacks" which render all of the unused dispensers electrically "hot" whenever the switch of any one dispenser is closed. In the event it becomes necessary to remove a fuel dispenser from service for purposes of maintenance, repair, or to avoid the creation of a hazardous condition following, for example, an accidental collision between an automobile and a dispenser, the potential for the occurrence of such feedbacks requires that each of the remaining, functioning dispensers, which are connected to the common relay, be shut down also. In a busy station, the need to shut down otherwise fully functional dispensers can have serious adverse economic consequences for the filling station operator.
To avoid the development of such undesirable feedbacks, individual relays, coupled to a common relay for actuating a single submersible pump, can be individually controlled by the switches associated with each hose or dispenser. Although effective, the cost of the relays and additional wiring associated with this approach can be considerable.
In view of the foregoing, it is a general object of the invention to provide a new and improved electrical controller for controlling several electrical devices in response to control inputs received from several sources.
It is a further object of the present invention to provide an electrical controller wherein undesirable feedbacks to unactuated ones of the control input sources are avoided.
It is still another object of the present invention to provide an electrical controller which can be implemented without considerable expense in terms of parts, time and labor.